Installation: Marley OLS+u Ultrasonic Oil Level Switch User Manual

Overview

The OLS+u Ultrasonic Oil Level Switch is designed to monitor low oil conditions in a cooling tower gearbox. It uses an oil-immersed ultrasonic sensing probe and changes relay state when the oil level falls below the factory-set monitoring point.

This device is intended for cooling tower operators, controls contractors, maintenance technicians, and building management system integrators. Its primary purpose is to generate an alarm for the operator. It should not normally be used as a shutdown circuit for the cooling tower fan motor.

The OLS+u package includes an ultrasonic DC level switch, an integrated cable, and an AC-to-DC interface box for installations where suitable DC power is not available. A separate OLS+u+BMS configuration is available when the BMS or PLC supplies the sensor power and accepts the relay signal directly.

Specifications

• Product: Marley OLS+u ultrasonic oil level switch
• Sensor: Flowline Switch-Tek LU10-2305 ultrasonic switch
• Power supply: 12 to 36 VDC for the ultrasonic sensor
• Sensor consumption: 25 mA maximum
• Interface-box supply: 90 to 264 VAC, single phase, 50/60 Hz
• Sensor contact: SPST relay with selectable normally open or normally closed operation
• Sensor contact rating: 60 VA, with a maximum of 125 VAC and 1 A
• Interface-box relay output: Two Form C dry contacts
• Interface-box contact rating: 7 A
• Sensor cable: Four-conductor, shielded, #22 AWG cable
• Standard cable length: 25 feet (7.6 m); a 50-foot lead is available for larger towers
• Maximum cable extension: Up to 1,000 feet using well-insulated, shielded, 14 to 20 AWG four-conductor cable
• Process connection: 3/4-inch NPT
• Process temperature: -40°F to 176°F (-40°C to 80°C)
• Pressure rating: 150 psi (10 bar) at 25°C, derated above that temperature
• Sensor enclosure rating: NEMA 4X, equivalent to IP65
• Sensor material: PFA
• Accuracy in water: ±1 mm
• Repeatability in water: ±0.5 mm
• Interface-box enclosure: NEMA 4X fiberglass enclosure

Detailed Description

The OLS+u Ultrasonic Oil Level Switch uses two miniature piezoelectric transducers positioned across a sensing gap. One transducer emits an ultrasonic signal at approximately 1.5 MHz, while the other receives it. The speed of sound across the gap changes when the gap contains oil instead of air. The electronics use this change to determine whether the probe is wet or dry.

The switch is installed in the gearbox oil-level piping. Its factory-set height establishes the low-oil alarm point, so normal installation does not require electrical calibration. A sliding height-adjustment bracket allows the installer to make a final mechanical adjustment when necessary.

The sensor is a four-wire device. The red and black conductors provide DC power, while the green and white conductors connect to the internal relay. Reversing the DC polarity on the red and black wires selects the relay’s normally open or normally closed operating arrangement.

In the AC-powered configuration, the interface box converts the incoming utility supply to DC power for the sensor. Its two Form C relay contacts connect the low-oil alarm circuit to a BMS or PLC. An internal pilot light illuminates when the sensor detects a low-oil condition.

The sensor is designed so oil can drain from the sensing gap as the level falls. This allows the probe to transition from wet to dry and initiate the low-level indication.

Safety

Read and understand the installation and operating instructions before installing, wiring, servicing, or testing the switch. Keep the manual available for future maintenance work.

• Turn off power at the control panel before servicing the sensor, interface box, or connected control circuit.
• If the disconnect is not within sight of the work area, apply an approved lockout procedure.
• Only qualified personnel should install, maintain, or repair the electrical equipment.
• Verify proper grounding, branch-circuit protection, conductor sizing, and access to the control panel before commissioning.
• Never apply more than 36 VDC to the ultrasonic sensor.
• Complete electrical work according to applicable national, state, local, and site codes.
• A special controller is required when the sensor is used in a hazardous location.
• The AC-to-DC interface box is not rated for hazardous-location applications.
• Keep interface-box wiring entries at the bottom of the enclosure.
• Seal conduit interiors to form a vapor barrier and prevent condensation from entering the enclosure.
• Do not use the low-oil switch as the primary shutdown circuit for the cooling tower fan motor.

Setup and Operation

Installing the Sensor

1. Confirm that the gearbox oil piping and mounting location match the supplied switch arrangement.
2. Install the sensor in the oil-level piping using the supplied mounting fittings.
3. Position the sensor so oil can drain from the sensing gap when the probe becomes dry.
4. Use the sliding bracket to make any required height adjustment relative to the gearbox.
5. Provide enough cable slack for installation, removal, inspection, and future service.

Connecting the DC Sensor

The sensor requires 12 to 36 VDC. For a normally open DC load, connect red to positive and black to negative. Connect the load through the green and white relay conductors according to the control circuit design.

For normally closed operation, reverse the sensor supply polarity: connect black to positive and red to negative. The green conductor is the relay common, and the white conductor serves as the switched contact. Confirm the required alarm logic before energizing the circuit.

The sensor may also be integrated as a P-channel or N-channel-style output using the appropriate jumper arrangement. Follow the control-system wiring design and verify polarity before applying power.

Connecting an AC Load

When switching an AC load through the sensor relay, power the sensor from a suitable 12 to 36 VDC source. Route the AC hot conductor through the relay contact and connect the AC neutral to the white conductor as required by the circuit. Use the normally open or normally closed polarity arrangement that matches the alarm logic.

Do not exceed the sensor relay’s rated load. For larger control systems, use the relay output to operate an appropriately rated intermediate control circuit.

Using the Interface Box

1. Provide a 90 to 264 VAC, single-phase, 50/60 Hz supply protected by the installation’s disconnect and branch-circuit equipment.
2. Route all incoming and outgoing wiring through the bottom of the enclosure.
3. Use copper conductors rated for at least 75°C and strip field wires approximately 3/8 inch where required by the terminal strip.
4. Connect the LU10 sensor cable to the interface-box terminals, matching the red, black, white, and green conductors.
5. Connect the dry relay contacts to the BMS, PLC, or alarm circuit.
6. Seal conduit openings internally with silicone or expanding foam to reduce moisture and condensation entry.
7. Close and latch the enclosure so the gasket forms a weather-resistant seal.

When the interface box is energized and the sensor detects low oil, the internal relay indicator light turns on. When the oil level is normal, the light remains off and the relay returns to its non-alarm condition.

Testing the Installation

1. Turn on power to the controller or DC power supply.
2. Immerse the sensing tip in a container of similar oil until the sensing gap is covered.
3. Move the probe between wet and dry conditions while observing the controller indicator or measuring the relay signal.
4. Use a voltmeter or ammeter if the controller has no input indicator.
5. Observe the level at which the relay changes state and adjust the sensor height if the alarm point is not correct.

When wired for normally open operation, a resistance meter should indicate an open circuit while the sensor is dry and a small resistance when the sensing tip is wet.

Cleaning and Maintenance

The ultrasonic switch does not require routine maintenance. During scheduled cooling tower service, inspect the probe, cable, mounting connection, conduit, and interface-box enclosure for physical damage, loose connections, moisture, or signs of oil leakage.

Keep the sensing gap free of deposits that could prevent the probe from becoming fully wet or dry. If cleaning is necessary, de-energize the equipment first and use a method compatible with the sensor material and the gearbox oil. Do not pull on the integrated cable when removing the sensor.

The sensor lead is molded into the ultrasonic switch and is not designed to be replaced separately. Coil excess cable rather than cutting it shorter whenever practical.

Troubleshooting

The Low-Oil Alarm Does Not Operate

• Confirm that the sensor is receiving between 12 and 36 VDC.
• Check the red and black power conductors for reversed or loose connections.
• Inspect the green and white relay conductors and verify that the selected normally open or normally closed arrangement matches the BMS input.
• Check the interface-box fuse, supply voltage, terminal connections, and relay indicator if the AC-to-DC package is used.
• Verify that the sensor tip is positioned at the intended alarm height.

The Alarm Remains Active

• Check the gearbox oil level using the approved oil-level indication method.
• Inspect the sensing gap for residue or an obstruction that could prevent proper wet/dry detection.
• Confirm that the probe is not installed above the intended oil level or positioned so oil cannot drain from the gap.
• Check the interface-box relay indicator. A light that remains on indicates that the sensor is detecting a dry, low-oil condition.

Checking the Interface-Box Relay

Use a continuity tester with the control panel de-energized before checking relay contacts. With power off, the internal relay light should be off. With the panel energized, the light should remain off when the sensor is wet and should turn on when the sensor is dry. A dry sensor corresponds to the low-oil condition.

Parts and Configurations

• Marley IBLU10 AC-to-DC interface box in a NEMA 4X fiberglass enclosure
• Marley IBLU10 AC-to-DC interface box in a NEMA 4X stainless-steel enclosure
• LU10 ultrasonic switch with a 25-foot cable
• LU10 ultrasonic switch with a 50-foot cable
• Relay and base assembly with two Form C contacts and an indicating light
• AC-to-DC power supply

Pros & Cons

• Pros: Ultrasonic wet/dry detection, factory-set sensing height, selectable relay logic, BMS compatibility, outdoor-rated sensor cable, and a weather-resistant interface-box option.
• Pros: The interface box provides isolated dry relay contacts and a visible low-oil indicator for commissioning and troubleshooting.
• Cons: The sensor requires a suitable 12 to 36 VDC supply or the matching AC-to-DC interface box.
• Cons: The integrated sensor cable cannot be replaced independently, and hazardous-location installations require suitable associated equipment and controls.